Which laboratory test should initially be ordered for a patient with chronic diarrhea and greasy stools that worsen with certain foods, suggesting malabsorption?

• A. Anti-endomysial antibodies
• B. Anti-mitochondrial antibodies
• C. Anti-glomerular basement membrane antibodies
• D. Anti-phospholipid antibodies

Answer: (A)

When there is fat malabsorption suggested by chronic diarrhea and steatorrhea that worsens with certain foods, screening for celiac disease is a key first step. Anti-endomysial antibodies (IgA) are highly specific for celiac disease and are commonly used as an initial serologic screen. A positive result would lead you to confirm with a duodenal biopsy showing villous atrophy, crypt hyperplasia, and intraepithelial lymphocytosis. The other antibodies target conditions that do not explain fat malabsorption: anti-mitochondrial antibodies are linked to primary biliary cholangitis, anti-glomerular basement membrane antibodies to Goodpasture syndrome, and anti-phospholipid antibodies to antiphospholipid syndrome. So the anti-endomysial antibody test best fits and guides the next steps in evaluating suspected malabsorption due to celiac disease.